Some radio-frequency power sensors employ thermocouples in order to measure power at the higher levels, e.g., from about -20 dBm to about +20 dBm. However, these thermocouple sensors are not satisfactory for measuring power in the lower level ranges, below about -20 dBm. Power sensors employing diodes are often used for measuring power in this lower level range, but such diode sensors have disadvantages for measuring power in the higher ranges.
As a result, the prior art has required the use of two separate sensors to cover accurately the entire range from about -70 dBm to +20 dBm. In an automated system these two sensors often have been connected to the measuring port simultaneously by means of a broad-band, precision radio-frequency power splitter. The losses of the power splitter were usually about six decibels, and these losses raised the lower level of the operating range of the low-level sensor. Moreover, additional error correction was required to account for the introduction of the splitter.
Another scheme from the prior art is to use a low power level diode type sensor at the high power levels also, and then apply correction factors to account for departures from a true square-law characteristic. This scheme does not truly measure power at the high levels, resulting in errors, which are influenced by the waveform of the signal being measured.
An object of the present invention is to increase the accuracy over a wide range of power measurement.
Another object of the invention is to provide a power measuring system with a wide dynamic range which successfully combines into a single instrument both a high power level sensing element and a low power level sensing element.
Another object of the invention is to provide a superior wide dynamic range radio-frequency power sensor, which is substantially unaffected by ambient temperatures.
A further object of the invention is to provide a wide dynamic range radio-frequency power sensor in which a switch-over between a high power level sensing element and a low power level sensing element is achieved without loss of stability or accuracy and without disturbing the input radio-frequency port.
A further object of the invention is to provide a wide range radio-frequency power sensor which is a true square-law device whose accuracy is unaffected by the waveform of the signal being measured.